package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Proxy;
import java.lang.reflect.Type;
import java.util.List;

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementid, Object... params) throws Exception {

        //将要去完成对simpleExecutor里的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementid, Object... params) throws Exception {
        List<Object> objects = selectList(statementid, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }


    }

    @Override
    public int insert(String statementId, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        int affectedRows = simpleExecutor.insert(configuration, mappedStatement, params);
        return affectedRows;
    }

    @Override
    public int update(String statementId, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        int affectedRows = simpleExecutor.update(configuration, mappedStatement, params);
        return affectedRows;
    }

    @Override
    public int delete(String statementId, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        int affectedRows = simpleExecutor.delete(configuration, mappedStatement, params);
        return affectedRows;
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回

        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, (proxy, method, args) -> {
            // 底层都还是去执行JDBC代码 //根据不同情况，来调用selctList或者selectOne
            // 准备参数 1：statmentid :sql语句的唯一标识：namespace.id= 接口全限定名.方法名
            // 方法名：findAll
            String methodName = method.getName();
            String className = method.getDeclaringClass().getName();

            String statementId = className + "." + methodName;

            MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
            switch (mappedStatement.getSqlCommond()) {
                case SELECT:
                    return this.query(method, statementId, args);
                case INSERT:
                    return this.insert(statementId, args);
                case UPDATE:
                    return this.update(statementId, args);
                case DELETE:
                    return this.delete(statementId, args);
                default:
                    throw new RuntimeException("Unknown execution method for: " + mappedStatement.getSqlCommond().name());
            }

        });

        return (T) proxyInstance;
    }

    private Object query(Method method, String statementId, Object... args) throws Exception {
        // 准备参数2：params:args
        // 获取被调用方法的返回值类型
        Type genericReturnType = method.getGenericReturnType();
        // 判断是否进行了 泛型类型参数化
        if (genericReturnType instanceof ParameterizedType) {
            List<Object> objects = selectList(statementId, args);
            return objects;
        }

        return selectOne(statementId, args);
    }


}
